Epoxy resins are widely known and used primarily as surface-coating materials because of their toughness, flexibility, adhesion and chemical resistance. They can be used for molding and laminating to produce glass fiber-reinforced articles. Use of epoxy resins in casting, potting and encapsulation in the electrical and tooling industries is also known.
Epoxy resins are fundamentally polyethers and are typically prepared by condensing epichlorohydrin with an aromatic diol such as bisphenol A. The epoxy resins then are cured by reaction with a polyamine. Representative patents which describes various epoxy resins and amine curing agents are as follows:
U.S. Pat. No. 4,447,586 discloses polyepoxide resins cured with hindered aromatic amines with the cure being accelerated by the incorporation of metal fluoroborates. Hindered aromatic amines utilized in the cure include diethyltoluenediamine derivatives, e.g., 1-methyl-3,5-diethyl-2,4- and 2,6-diaminobenzene; methylene bis(2,6-diisopropylaniline), methylene bis(2,6-diethylaniline) and the like. The epoxide resins are reported as having excellent heat distortion temperature resistance and excellent resistance to water and steam.
U.S. Pat. No. 2,817,644 discloses various polyepoxide resin systems formed by reacting glycidyl polyethers of polyhydric phenols with a hydrogenated aromatic primary or secondary amine. The use of hydrogenated aromatic amines enhances processability in that the curing agents are liquid and they have little odor or toxicity. Unexpectedly high hot hardness, excellent resistance to solvents and water and good adhesion to metals are reported. Examples of aromatic polyamines which when hydrogenated form candidate curing agents include phenylenediamine isomers, N-methylphenylenediamine isomers. 2.4-diaminotoluene, 1,3-diamino-4-isopropylbenzene and the like.
U.S. Pat. No. 3,629,181 discloses the use of cycloaliphatic di-primary diamines as curing agents for epoxide resins formed by the reaction of a glycidyl ether with a polyhydric phenol. In the prior art section, the patentees pointed out that cycloaliphatic or cycloaliphatic-aliphatic polyamines had been utilized to cure epoxide resins, but surface faults such as orange peel and frosting occurred. Other problems with respect to solvent resistance and sweating were reported. Di-primary amines used in forming adducts for curing polyepoxide resins included cyclohexane and alkyl substituted cyclohexanes, such as 4-ethyl-1,2-diaminocyclohexane, 4,4'-diaminodicyclohexylmethane(PACM) and isophoronediamine.
U.S. Pat. No. 3,321,438 discloses polyepoxide resins suited for fluidized bed coating applications. The polyepoxide systems having vicinal epoxy equivalency are cured with aliphatic amines and piperazines under controlled conditions. Examples of amine curing agents include diethylenetriamine, dimethylamino- and diethylaminopropylamine, propylenediamine, triethylenetetramine; and cycloaliphatic diamines such as N-cyclohexyl-1,3-propane iamine and N-aminoethylpiperazine.
U.S. Pat. Nos. 3,631,125 and 3,741,928 disclose epoxide molding compositions containing metatoluenediamine. The examples show the use of 2,4-and 2,6-toluenediamine and mixtures as curatives for a diglycidylether of 2,2-bis(parahydroxyphenyl)propane epoxide resin.